The present invention relates to a dual polarised radiating element for a cellular base station antenna. Recently, the demand for antennas for mobile and wireless applications has increased dramatically. There are now a number of land based systems for wireless communications using a wide range of frequency bands.
Several cellular base station antenna manufacturers are proposing antennas having electrical dipoles located one quarter of a wavelength above a finite ground plane formed by a reflector. Dual polarisation is achieved by way of orthogonal linear polarisation obtained by excitation of the respective, mutually perpendicular electrical dipoles. These electrical dipoles are slanted 45° in opposite directions relative to the central longitudinal axis of the reflector.
Unfortunately, such antennas provide limited far field pattern performance: the horizontal 3dB HPBW (for Half Power Beam Width) stability faces large variation (for instance 65°+/−6°), the cross-polarisation level (for example the cross-polar discrimination at +/−60° about 5 dB) is too high across passbands up to 25% (for example 806-960MHz or 1700-2200MHz).
Document US2006/0109193 discloses an antenna improving the 3 dB HPBW stabilisation. Moreover, this antenna also reduces the cross-polarisation level. This antenna comprises an array of dual polarized radiating elements mounted on a reflector structure for reflecting polarised radiofrequency signals. The reflector structure has a pyramidal or conical horn-like shape for each radiating element.
This antenna design significantly increases the manufacturing costs, since horn-like shapes require the design of specific moulds.
In order to reduce the cross-polarisation level, other designs include lateral elongated choke reflectors fixed on both sides of a reflector. These designs lead to complex and costly manufacturing processes.